Using vault to track reception of slices

ABSTRACT

A method for execution by one or more processing modules of one or more computing devices of a dispersed storage network (DSN) begins by detecting, by an access module, a write failure of an encoded data slice to a storage unit of a set of DSN storage units. The method continues when detecting the write failure, by adding by the access module, an error entry to an error list. The method continues by recovering, by an integrity module, the error entry from the error list. The method continues by generating, by the integrity module, a rebuilt encoded data slice for the encoded data slice of the write failure. The method continues by facilitating storage of the rebuilt encoded data slice in the storage unit associated with the write failure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §119(e) to U.S. Provisional Application No. 62/222,819,entitled “IDENTIFYING AN ENCODED DATA SLICE FOR REBUILDING,” filed Sep.24, 2015, which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

Technical Field of the Invention

This invention relates generally to computer networks and moreparticularly to dispersing error encoded data.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network (DSN) in accordance with the present invention; and

FIG. 9A is a flowchart illustrating an example of identifying an encodeddata slice for rebuilding in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 & 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data as subsequently described with reference to oneor more of FIGS. 3-8. In this example embodiment, computing device 16functions as a dispersed storage processing agent for computing device14. In this role, computing device 16 dispersed storage error encodesand decodes data on behalf of computing device 14. With the use ofdispersed storage error encoding and decoding, the DSN 10 is tolerant ofa significant number of storage unit failures (the number of failures isbased on parameters of the dispersed storage error encoding function)without loss of data and without the need for a redundant or backupcopies of the data. Further, the DSN 10 stores data for an indefiniteperiod of time without data loss and in a secure manner (e.g., thesystem is very resistant to unauthorized attempts at accessing thedata).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSTN memory 22for a user device, a group of devices, or for public access andestablishes per vault dispersed storage (DS) error encoding parametersfor a vault. The managing unit 18 facilitates storage of DS errorencoding parameters for each vault by updating registry information ofthe DSN 10, where the registry information may be stored in the DSNmemory 22, a computing device 12-16, the managing unit 18, and/or theintegrity processing unit 20.

The DSN managing unit 18 creates and stores user profile information(e.g., an access control list (ACL)) in local memory and/or withinmemory of the DSN memory 22. The user profile information includesauthentication information, permissions, and/or the security parameters.The security parameters may include encryption/decryption scheme, one ormore encryption keys, key generation scheme, and/or dataencoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particularuser, a user group, a vault access, public vault access, etc. Forinstance, the DSTN managing unit 18 tracks the number of times a useraccesses a non-public vault and/or public vaults, which can be used togenerate per-access billing information. In another instance, the DSTNmanaging unit 18 tracks the amount of data stored and/or retrieved by auser device and/or a user group, which can be used to generateper-data-amount billing information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSTN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 60 is shown inFIG. 6. As shown, the slice name (SN) 60 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

As discussed in greater detail below, in association with FIGS. 9 and9A, when a DS processing unit fails to write a slice to a given store,it may place an entry into a dispersed data structure (DSN memory) suchas a Dispersed Lockless Concurrent Index (DLCI), a queue, or even simplya dedicated vault for the given DS unit. As an alternative to performingrebuild list scanning, a rebuild module may simply consult thisdispersed data structure to find entries for slices that were notsuccessfully written to the store (e.g., slice names within thenamespace range owned by that particular DS unit). When an entry isfound, and processed by a rebuild module, the rebuild module can thenremove the entry from the dispersed data structure. Rebuild scanningwould then be a special case to handle cases of memory devicedestruction, bin file corruption, file system corruption, etc., ratherthan a continuous process.

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network (DSN) that includes the distribute storage and task(DST) processing unit 16 of FIG. 1, the DST integrity processing unit 20of FIG. 1, the network 24 of FIG. 1, and a storage set. Storage set 902includes a set of DST execution (EX) units 1-n. Each DST execution unitmay be implemented utilizing the DST execution unit 36 of FIG. 1.Hereafter, each DST execution unit may be interchangeably referred to asa storage unit and the storage set may be interchangeably referred to asa set of storage units (set of DSN storage units). The DSN functions toidentify an encoded data slice for rebuilding.

In an example of operation of the identifying of the encoded data slicefor rebuilding, the DST processing unit 16 detects a write failure ofencoded data slice, where the DST processing unit 16 dispersed storageerror encodes a data object to produce a plurality of sets of encodeddata slices, issues, via the network 24, write slice requests A1-An tostorage units of the storage set 902, and interprets received writeslice responses 900 to identify the write failure (e.g., interpreting anunfavorable write response or detecting, within a time frame, that anexpected write responses has not been received). For example, the DSTprocessing unit 16 detects that the encoded data slice A3 to be storedin DST execution unit 3 has failed to be stored thus producing the writefailure.

When detecting the write failure, the DST processing unit 16 adds anerror entry to an error list (e.g., stored within memory of DSTintegrity processing unit 20). The adding includes generating a newerror entry that includes one or more of a slice name associated withthe write failure, an encoded data slice associated with the writefailure, an identifier of a storage unit associated with the writefailure; and updating the error list to include the new error entry. Forexample, the DST processing unit 16 dispersed storage error encodes thenew entry to produce a set of error entry slices EE1-EEn, issues, viathe network 24, write slice requests EE1-EEn to the storage unit of thestorage set, where the write slice requests include the set of errorentry slices. Alternatively, or in addition to, the DST processing unit16 updates the error list by updating and/or adding a new entry of adispersed hierarchical index stored as a plurality of node objectswithin the storage set utilizing node encoded slices.

With the error entry added to the error list, the DST integrityprocessing unit 20 recovers the new entry from the error list. Forexample, the DST integrity processing unit 20 issues, via the network24, read slice requests for the error entry slices, receives read sliceresponses EE1-EEn that includes at least the decode threshold number ofthe error entry slices, and dispersed storage error decodes the receiveddecode threshold number of error entry slices to reproduce the newentry.

Having recovered the new entry from the error list, a DST integrityprocessing unit 20 generates a rebuilt encoded data slice for the writefailure based on the recovered new entry. For example, the DST integrityprocessing unit 20 identifies the encoded data slice to be rebuilt(e.g., extract a slice name A3 from the recovered new entry), issuesread slice requests for the encoded data slices, receives read sliceresponses A1-An that includes at least a decode threshold number ofencoded data slices of a set of encoded data slices associated withencoded data slice to be rebuilt, dispersed storage error decodes thereceived decode threshold number of encoded data slices to reproduce adata segment, and dispersed storage error encodes the data segment toproduce the rebuilt encoded data slice A3.

Having produced the rebuilt encoded data slice, the DST integrityprocessing unit 20 facilitates storage of the rebuilt encoded data slicein the storage unit associated with the write failure. For example, theDST data processing unit 20 issues, via the network 24, a write slicerequest A3 to the DST execution unit 3, where the write slice requestincludes the rebuilt encoded data slice A3. Alternatively, or inaddition to, the DST integrity processing unit 20 deletes the set oferror entry slices when confirming successful storage of the rebuiltencoded data slice. For example, the DST integrity processing unit 20receives a favorable write slice response A3 and issues a delete slicerequests EE1-EEn to the set of DST execution units 1-n.

When a DS processing unit fails to write a slice to a given store, itmay place an entry into a dispersed data structure such as a DispersedLockless Concurrent Index (DLCI), a queue, or even simply a dedicatedvault for the given DS unit. As an alternative to performing rebuildlist scanning, a rebuild module may simply consult this dispersed datastructure to find entries for slices that were not successfully writtento the store (e.g., slice names within the namespace range owned by thatparticular DS unit). When an entry is found, and processed by a rebuildmodule, the rebuild module can then remove the entry from the disperseddata structure. Rebuild scanning would then be a special case to handlecases of memory device destruction, bin file corruption, file systemcorruption, etc., rather than a continuous process.

FIG. 9A is a flowchart illustrating an example of synchronizingreplication of stored data. In particular, a method is presented for usein conjunction with one or more functions and features described inconjunction with FIGS. 1-2, 3-8, and also FIG. 9.

As shown the flowchart illustrates an example of identifying an encodeddata slice for rebuilding. The method begins or continues at step 904where an access module of one or more processing modules of one or morecomputing devices of a dispersed storage network detects a write failureof an encoded data slice to a storage unit of a set of storage units,where the access module dispersed storage error encodes a data object toproduce a plurality of sets of encoded data slices, issues read slicerequests to the storage unit of the storage set, and interprets writeslice responses to identify the write failure (e.g., no response fromthe storage unit within a storage time frame or receiving an unfavorableresponse from the storage unit).

When detecting the write failure, the method continues at step 906 wherethe access module adds an error entry to an error list. For example, theaccess module generates a new entry that includes one or more of: aslice name associated with the write failure, an encoded data sliceassociated with the write failure, or an identifier of the storage unit;and updates the error list to include the new entry. The updatingincludes at least one of a dispersed storage error encoding the newentry to produce a set of error entry slices, issuing write slicerequests to the set of storage units, where the write slice requestsincludes the set of error entry slices; and updating an entry of adispersed hierarchical index.

The method continues at step 908 where and integrity module of theplurality of processing modules recovers the error entry from the errorlist. For example, the integrity module issues read slice requests tothe set of storage units, receives read slice responses that includes atleast a decode threshold number of the error entry slices, and dispersedstorage error decodes the error entry slices to reproduce the errorentry. As another example, the integrity module recovers a correspondingnode of the dispersed hierarchical index and extracts the error entryfrom the recovered node.

The method continues at step 910 where the integrity module generates arebuilt encoded data slice for the encoded data slice of the writefailure. For example, the integrity module identifies the encoded dataslice to be rebuilt (e.g., extracting the slice name from the recoverederror entry), issues read slice requests to the set of storage units,receives read slice responses that includes at least the decodethreshold number of encoded data slices of a set of encoded data slicesassociated with the encoded data slice to be rebuilt, dispersed storageerror decodes the decode threshold number of received encoded dataslices to reproduce a data segment, and dispersed storage error encodesthe reproduced data segment to produce the rebuilt encoded data slice.

The method continues at step 912 where the integrity module facilitatesstorage of the rebuilt encoded data slice in the storage unit associatedwith the write failure. For example, the integrity module issues a writeslice request to the storage unit, where the write slice requestincludes the rebuilt encoded data slice. Alternatively, or in additionto, the integrity module facilitates, in step 914, deletion of the errorentry from the error list when successfully facilitating the storage ofthe rebuilt encoded data slice (e.g., deleting the error entry slices,deleting the entry of the node of the dispersed hierarchical index).

The method described above in conjunction with the processing module canalternatively be performed by other modules of the dispersed storagenetwork or by other computing devices. In addition, at least one memorysection (e.g., a non-transitory computer readable storage medium) thatstores operational instructions can, when executed by one or moreprocessing modules of one or more computing devices of the dispersedstorage network (DSN), cause the one or more computing devices toperform any or all of the method steps described above.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method for execution by one or more processingmodules of one or more computing devices of a dispersed storage network(DSN), the method comprises: detecting, by an access module of the oneor more processing modules, a write failure of an encoded data slice toa storage unit of a set of DSN storage units; when detecting the writefailure, adding by the access module, an error entry to an error list;recovering, by an integrity module of the one or more processingmodules, the error entry from the error list; generating, by theintegrity module, a rebuilt encoded data slice for the encoded dataslice of the write failure; and facilitating storage of the rebuiltencoded data slice in the storage unit associated with the writefailure.
 2. The method of claim 1, wherein detecting the write failureincludes the access module dispersed storage error encoding a dataobject to produce a plurality of sets of encoded data slices, issuingread slice requests to the storage unit of the storage set, andinterpreting write slice responses to identify the write failure.
 3. Themethod of claim 1, wherein the error entry list is stored in any of: adispersed data structure, a Dispersed Lockless Concurrent Index (DLCI),a queue, or a dedicated storage vault.
 4. The method of claim 1, whereinthe write failure is detected by any of: receiving no response from thestorage unit within a storage time frame or receiving an unfavorableresponse from the storage unit.
 5. The method of claim 1, wherein addingthe error entry includes the access module generating a new error entrythat includes one or more of: a slice name associated with the writefailure, an encoded data slice associated with the write failure, or anidentifier of the storage unit.
 6. The method of claim 1, wherein therecovering includes: a dispersed storage error encoding a new entry toproduce a set of error entry slices, issuing write slice requests to theset of DSN storage units, where the write slice requests includes theset of error entry slices; and updating an entry of a dispersedhierarchical index.
 7. The method of claim 1, wherein the recoveringincludes the integrity module issuing read slice requests to the set ofDSN storage units, receiving read slice responses that include at leasta decode threshold number of the error entry slices, and dispersedstorage error decoding the error entry slices to reproduce the errorentry.
 8. The method of claim 1, wherein the recovering includes theintegrity module recovering a corresponding node of a dispersedhierarchical index and extracting the error entry from the recoveredcorresponding node.
 9. The method of claim 1, wherein the generatingincludes the integrity module identifying the encoded data slice to berebuilt by: issuing read slice requests to the set of DSN storage units,receiving read slice responses that includes at least the decodethreshold number of encoded data slices of a set of encoded data slicesassociated with the encoded data slice to be rebuilt, disperse storageerror decoding the at least decode threshold number of received encodeddata slices to reproduce a data segment, and disperse storage errorencoding the reproduced data segment to produce the rebuilt encoded dataslice.
 10. The method of claim 1, wherein facilitating includes theintegrity module issuing a write slice request to the storage unit,where the write slice request includes the rebuilt encoded data slice.11. The method of claim 1, wherein facilitating further comprisesdeletion of the error entry from the error list when successfullyfacilitating the storage of the rebuilt encoded data slice.
 12. Themethod of claim 11, wherein the deletion includes any of: deletingencoded data slices of the error entry or deleting an entry of a node ofa dispersed hierarchical index.
 13. A processing unit within a dispersedstorage network (DSN) comprises: an interface; a local memory; and aprocessing module operably coupled to the interface and the localmemory, wherein the processing module functions to: detect, by an accessmodule of the processing module, a write failure of an encoded dataslice to a storage unit of a set of DSN storage units; when detectingthe write failure, add by the access module, an error entry to an errorlist; recover, by an integrity module of the processing module, theerror entry from the error list; generate, by the integrity module, arebuilt encoded data slice for the encoded data slice of the writefailure; and facilitate storage of the rebuilt encoded data slice in thestorage unit associated with the write failure.
 14. The processing unitof claim 13, wherein detecting the write failure includes the accessmodule dispersed storage error encoding a data object to produce aplurality of sets of encoded data slices, issuing read slice requests tothe storage unit of the storage set, and interpreting write sliceresponses to identify the write failure.
 15. The processing unit ofclaim 13, wherein adding the error entry includes the access modulegenerating a new entry that includes one or more of: a slice nameassociated with the write failure, an encoded data slice associated withthe write failure, or an identifier of the storage unit.
 16. Theprocessing unit of claim 13, wherein the recovering includes: adispersed storage error encoding a new error entry to produce a set oferror entry slices, issuing write slice requests to the set of DSNstorage units, where the write slice requests includes the set of errorentry slices; and updating an entry of a dispersed hierarchical index.17. The processing unit of claim 13, wherein the recovering includes theintegrity module issuing read slice requests to the set of DSN storageunits, receiving read slice responses that include at least a decodethreshold number of the error entry slices, and dispersed storage errordecoding the error entry slices to reproduce the error entry.
 18. Theprocessing unit of claim 13, wherein the recovering includes theintegrity module recovering a corresponding node of a dispersedhierarchical index and extracting the error entry from the recoveredcorresponding node.
 19. The processing unit of claim 13, wherein thegenerating includes the integrity module identifying the encoded dataslice to be rebuilt by: issuing read slice requests to the set of DSNstorage units, receiving read slice responses that includes at least thedecode threshold number of encoded data slices of a set of encoded dataslices associated with the encoded data slice to be rebuilt, dispersestorage error decoding the at least decode threshold number of receivedencoded data slices to reproduce a data segment, and disperse storageerror encoding the reproduced data segment to produce the rebuiltencoded data slice.
 20. The processing unit of claim 13, wherein theerror entry list is stored in any of: a dispersed data structure, aDispersed Lockless Concurrent Index (DLCI), a queue, or a dedicatedstorage vault.